Allow to use HeapTupleData embedded in [Buffer]HeapTupleTableSlot.

That avoids having to care about the lifetime of the
HeapTupleHeaderData passed to ExecStore[Buffer]HeapTuple(). That
doesn't make a huge difference for a plain HeapTupleTableSlot, but for
BufferHeapTupleTableSlot it can be a significant advantage, avoiding
the need to materialize slots where it's inconvenient to provide a
HeapTupleData with appropriate lifetime to point to the on-disk tuple.

It's quite possible that we'll want to add support functions for
constructing HeapTuples using that embedded HeapTupleData, but for now
callers do so themselves.

Author: Andres Freund
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de

diff --git a/src/include/executor/tuptable.h b/src/include/executor/tuptable.h
index 8da0b84dd7e9c1909d97f02384cc144464ba8fd0..1e94beafac5b84601200b40fe39383b9b17c6a78 100644 (file)
--- a/src/include/executor/tuptable.h
+++ b/src/include/executor/tuptable.h
@@ -16,6 +16,7 @@
 
 #include "access/htup.h"
 #include "access/tupdesc.h"
+#include "access/htup_details.h"
 #include "storage/buf.h"
 
 /*----------
@@ -246,6 +247,7 @@ typedef struct HeapTupleTableSlot
        HeapTuple       tuple;          /* physical tuple */
 #define FIELDNO_HEAPTUPLETABLESLOT_OFF 2
        uint32          off;            /* saved state for slot_deform_heap_tuple */
+       HeapTupleData tupdata;  /* optional workspace for storing tuple */
 } HeapTupleTableSlot;
 
 /* heap tuple residing in a buffer */